Arizona State University chemists have demonstrated a nanotech version of molecular self-regulation by designing a molecule that mimics the way in which plants defend themselves from an overload of sunshine by draining away the excess light energy as heat so that it can not generate destructive high energy intermediates. The nanotech molecule is composed of five components, one of which responds to light by reversibly changing shape. Excerpts from “Molecule With ‘Self-control’ Synthesized“:

…The ASU-designed molecule works in a similar fashion in that it converts absorbed light to electrochemical energy but reduces the efficiency of the conversion as light intensity increases. The ASU-designed molecule has several components including two light gathering antennas— a porphyrin electron donor, a fullerene acceptor and a control unit that reversibly photoisomerizes between a dihydroindolizine (DHI) and a betaine (BT).

When white light (sunlight) shines on a solution of the molecules, light absorbed by the porphyrin (or by the antennas) is converted to electrochemical potential energy. When the white light intensity is increased, the DHI on some molecules change to a different molecular structure, BT, that drains light excitation energy out of the porphyrin and converts it to heat, avoiding the generation of excess electrochemical potential. As the light becomes brighter, more molecules switch to the non-functional form, so that the conversion of light to chemical energy becomes less efficient. The molecule adapts to its environment, regulating its behavior in response to the light intensity.

…The research is also important to one aspect of the exploding field of nanotechnology, that of regulation, [ASU chemist Devens] Gust adds. Biological systems are known for their ability to engage in adaptive self-regulation. The nanoscale components respond to other nanoscale systems and to external stimuli in order to keep everything in balance and functioning properly. The ASU research shows how a bio-regulation system has been captured in a non-biological molecular scale analog process.

“Achieving such behavior in human-made devices is vital if we are to realize the promise of nanotechnology,” adds Gust. “Although the mechanism of control used in the ASU molecule is different from that employed in [the plant system], the overall effect is the same as occurs in the natural photosynthetic process.”